The timing and cause of the extinction that killed
all animals heavier than 60 kg in Australia has been elusive. Using
ratites' (flightless birds) eggshells, we have been able to narrow
the time window of the extinction to 50,000 +/- 5,000 years ago.
Other research has since supported our age estimate for this extinction
(Roberts et al., 2001). We have also used the eggshells of these
birds to understand dietary changes through time and from region
to region. Stable isotopes of carbon, nitrogen and oxygen are preserved
in the crystal matirx of the eggshells and present us with a proxy
of diet. Based on the evidence to date, our hypothesis is that after
human colonization of Australia (60,000 years ago), the ecosystem
changed due to over-burning of the landscape. This would have reduced
evapotranspiration over the interior of the continent, thereby increasing
aridity and eliminating food supplies for the large animals. (learn
more)

The Racemization of Amino Acids in Charophyte
Oogonia:

Charophytes, a type of green algae, are prevalent
both in the modern and fossil lacustrine environments of Australia
and elsewhere. They generally tolerate a wide range of water conditions,
which might explain their ubiquity. Some species (e.g., Lamprothamnium
papulosum) create a calcareous shell (oogonium) around the
female gamete (oospore). These shells are about the size of coarse
sand, but are fairly robust for their size and manage to preseve
well in the fossil record. This project aimed to determine if oogonia
are a viable source of sample material for amino acid geochronology.
The racemization rate for each amino acid in a given taxon must
be calculated in order to understand the age or thermal history
of a sample. So, this was a primary thrust of the project. Then,
site-specific chronologies and thermal histories were hoped to be
calculated, which would give us more insight into the lake level
histories in central Australia. In short, oogonia do not appear
to be extremely useful for amino acid geochronology due to wide
ranges of D/L ratios and amino acid concentrations within a single
stratum. Furthermore, D/L ratio and concentration do not appear
to be related. This translates to enormous error bars associated
with age or paleotemperature estimates. (learn
more)

Related Projects

The Late Quaternary Glacial
History of Baffin Island:

Ice
sheets are an integral part of the Earth’s climate system,
but the chronology and dynamics of Pleistocene ice sheets is in
most places only loosely constrained. In the Eastern Canadian Arctic,
for example, the history of the northeastern Laurentide Ice Sheet
(LIS) during the Last Glacial Maximum (LGM) is only known in selected
regions, but is extrapolated to broader areas. More than 160 cosmogenic
exposure ages from the Clyde Region, northeastern Baffin Island,
reveal that the northeastern LIS was more extensive and dynamic
than previously depicted. Tors on weathered uplands surrounding
Clyde Inlet are covered with perched erratics that have cosmogenic
exposure ages of 20-10 ka, indicating that the uplands were glaciated
by cold-based, non-erosive ice during the LGM. In contrast, warm-based,
erosive ice probably occupied Clyde Inlet throughout the LGM, indicating
strong gradients in basal thermal regimes and the operation of an
ice stream in Clyde Inlet. In the most distal sectors of the Clyde
Foreland, where cold-based ice hardly modified the landscape, erratics
yield a multi-modal exposure age distribution that may indicate
numerous advances and retreats of cold-based ice across the foreland
throughout Marine Isotope Stages 3 and 2. Ice retreated from the
Clyde Foreland ~13 ka, from the mouth of Clyde Inlet ~12-10 ka,
and had reached the fiord head by ~8.3 ka. Upland tors surrounding
outer Clyde Inlet have single-nuclide apparent exposure ages >60
ka. However, paired 26Al and 10Be concentration data reveal that
they are at least several hundred thousand years old, indicating
that while the uplands have been covered by ice off and on throughout
the Quaternary, they have only been slightly modified.
These new data depict an extensive LIS in the Clyde Region during
the LGM, possibly terminating at the continental shelf break beyond
Clyde Inlet. Strong gradients in basal thermal regimes suggest highly
variable patterns in glacier thickness, velocity, and erosion, an
overall pattern indicative of ice stream activity. A northeastern
LIS this dynamic and extensive would have been closely linked with
fluctuating ocean circulation and sea level.